Prilling

Prilling is a manufacturing process used to convert molten or liquid materials into small, spherical particles called prills. In the process, droplets are formed by atomization and fall through a stream of hot air or gas within a prilling tower or similar vessel, where they cool and solidify into uniform beads. The final prill size is controlled primarily by the nozzle or atomizer, feed rate, and the temperature, humidity, and velocity of the drying gas.

Process details: The material is heated to above its melting point or dispersed as a spray. Droplets exit the nozzle and descend through a drying zone where heat transfer and air flow cause rapid solidification. Prills are collected at the base or discharged through conveyors, with oversize or undersize products sorted by screening or air classification. The approach can be designed to minimize dust and promote consistent porosity and strength.

Equipment: The core equipment is a prilling tower, a tall vertical column where hot air or gas flows upward or downward. Nozzles or atomizers form droplets, and internal baffles or packing help control residence time and heat transfer. Auxiliary equipment includes heaters, fans, cyclones, filters, and screening or stacking systems for product sizing and collection.

Materials and applications: Prilling is widely used to produce fertilizers such as urea prills, ammonium nitrate prills, and ammonium phosphate prills, which benefit from good flowability and stability. Other applications include polymer beads, food-grade ingredients, and certain controlled-release products. Safety and regulatory considerations apply, especially when handling energetic or hazardous materials.

Advantages and limitations: Prills typically exhibit high sphericity and uniform size, good flow, and predictable dissolution. Limitations include energy-intense heating, moisture sensitivity, and capital costs for tower-based equipment.